There are various warnings when compiling the _multiprocessing extension in 64-bit mode under Windows. Many seem related to the fact that read() and friends under Windows take "int" size arguments rather than "size_t".

20>------ Build started: Project: _multiprocessing, Configuration: Release x64 ------
20>Compiling...
20>multiprocessing.c
20>win32_functions.c
20>socket_connection.c
20>..\Modules\_multiprocessing\socket_connection.c(32) : warning C4267: 'function' : conversion from 'size_t' to 'int', possible loss of data
20>..\Modules\_multiprocessing\socket_connection.c(54) : warning C4267: 'function' : conversion from 'size_t' to 'int', possible loss of data
20>..\Modules\_multiprocessing\socket_connection.c(126) : warning C4244: '=' : conversion from 'Py_ssize_t' to 'int', possible loss of data
20>..\Modules\_multiprocessing\socket_connection.c(137) : warning C4244: '=' : conversion from 'Py_ssize_t' to 'int', possible loss of data
20>..\Modules\_multiprocessing\socket_connection.c(145) : warning C4244: '=' : conversion from 'Py_ssize_t' to 'int', possible loss of data
20>z:\py3k\__svn__\modules\_multiprocessing\connection.h(139) : warning C4244: '=' : conversion from 'Py_ssize_t' to 'int', possible loss of data
20>z:\py3k\__svn__\modules\_multiprocessing\connection.h(183) : warning C4244: 'function' : conversion from 'Py_ssize_t' to 'int', possible loss of data
20>z:\py3k\__svn__\modules\_multiprocessing\connection.h(237) : warning C4244: 'function' : conversion from 'Py_ssize_t' to 'int', possible loss of data
20>z:\py3k\__svn__\modules\_multiprocessing\connection.h(285) : warning C4244: '=' : conversion from 'Py_ssize_t' to 'int', possible loss of data
20>z:\py3k\__svn__\modules\_multiprocessing\connection.h(323) : warning C4244: 'function' : conversion from 'Py_ssize_t' to 'int', possible loss of data
20>semaphore.c
20>pipe_connection.c
20>..\Modules\_multiprocessing\pipe_connection.c(24) : warning C4267: 'function' : conversion from 'size_t' to 'DWORD', possible loss of data
20>..\Modules\_multiprocessing\pipe_connection.c(50) : warning C4267: 'function' : conversion from 'size_t' to 'DWORD', possible loss of data
20>z:\py3k\__svn__\modules\_multiprocessing\connection.h(139) : warning C4244: '=' : conversion from 'Py_ssize_t' to 'int', possible loss of data
20>z:\py3k\__svn__\modules\_multiprocessing\connection.h(183) : warning C4244: 'function' : conversion from 'Py_ssize_t' to 'int', possible loss of data
20>z:\py3k\__svn__\modules\_multiprocessing\connection.h(237) : warning C4244: 'function' : conversion from 'Py_ssize_t' to 'int', possible loss of data
20>z:\py3k\__svn__\modules\_multiprocessing\connection.h(285) : warning C4244: '=' : conversion from 'Py_ssize_t' to 'int', possible loss of data
20>z:\py3k\__svn__\modules\_multiprocessing\connection.h(323) : warning C4244: 'function' : conversion from 'Py_ssize_t' to 'int', possible loss of data
20>Linking...
20>   Creating library Z:\py3k\__svn__\PCbuild\\amd64\\_multiprocessing.lib and object Z:\py3k\__svn__\PCbuild\\amd64\\_multiprocessing.exp
20>Generating code
20>Finished generating code
20>Build log was saved at "file://Z:\py3k\__svn__\PCbuild\x64-temp-Release\_multiprocessing\BuildLog.htm"
20>_multiprocessing - 0 error(s), 17 warning(s)